Lance Armstrong had not long announced his retirement from retirement before journalists and experts (two groups not always mutually inclusive) were queuing up to condemn his ego and wrong-headedness. "Those who had expected to see Lance Armstrong complete his return to competitive cycling by winning this summer's Tour de France can kiss their hopes goodbye. It isn't going to happen," wrote Lawrence Donegan in the Guardian in May. When Le Tour got underway, ITV's roving reporter Ned Boulting pronounced that he would pretty well eat his chapeau if the seven-times winner rode in triumph down the Champs-Elysées this year.

A fortnight into the three-week event, we are starting to realise that the only hill the 37-year-old is over is the Col du Tourmalet in the Pyrenees. The fact that he is still in contention is mind-blowing enough and he has already proved that, despite the evidence of Michael Jordan, Bjorn Borg and Muhammad Ali, it is possible for a sporting colossus to make a dignified comeback. He is even talking about competing in the Tour de France next year.

The sceptics might be less surprised to witness Armstrong's renaissance if they had read John Wilcockson's new biography. The book's breathless subtitle - "The World's Greatest Champion" (no question mark, no "probably") - reveals straight away that this is not going to be an excoriation of the most divisive man in sport. But then, there already exist plenty of accounts that set out to discredit Armstrong as a drug-addled cheat, although these have rarely found publishers outside France, a country that has as relaxed an approach to defamation as it does to dog poo in the streets.

In the US, this book is titled Lance: The Making of the World's Greatest Champion, which is more accurate, as Wilcockson's main intent is to put forward the non-pharmacological explanations for the American's record-obliterating achievements.

Armstrong admirers might wonder what scraps of personal history are left after his own inspirational, bestselling autobiographies It's Not About the Bike (2000) and Every Second Counts (2003). Wilcockson, an experienced journalist and editor on cycling magazines, who is currently following his 41st Tour de France, concentrates on the years leading up to Armstrong's diagnosis with testicular cancer at the age of 25, before he achieved his most formidable performances on the road.

The book is not authorised as such, but author and subject spoke several times during its creation and the cyclist bestowed "the opportunity to talk with people who otherwise might have been hesitant to speak openly about him". More than 60 friends and family have been interviewed, including some, notably his stepfather Terry, with whom Armstrong has not spoken since his teens.

This idea of permission is revealing - Armstrong is famed for his mental Rolodex of enemies, a record of anyone who has, to his mind, betrayed his trust. The defining moment in his professional career came in 2001 when he gave his great stooge, Jan Ullrich, what is universally known as "the Look", his cool blue eyes boring through the soul of the long-suffering German before he sprinted decisively up the side of an alp. (For the record, Armstrong denies here that there is anything to the Look; he was simply scanning the road for a team-mate. And if you believe that ... )

Certainly, there is a danger that Wilcockson will not submit his subject to the harshest scrutiny. The polarising effect of Armstrong's desire to not just win but crush his rivals is alluded to but no more. The book coyly describes a "conversation" that Armstrong had with a young French rider called Christophe Bassons in 1999. Bassons, nicknamed "Monsieur Propre" or "Mr Clean", for his anti-doping stance, was competing in his first Tour and cast doubt on Armstrong's performance in his daily column for Le Parisien; the next day, they had their discussion and shortly afterwards Bassons pulled out of the race, never to be seen at the top level again. There is no question of impropriety on Armstrong's part, but it is a brave person who goes to war with him.

Wilcockson would contend, however, that it is this belligerence and indomitable force of will that are responsible for his enduring success. In one of his earliest races, the 1989 world junior cycling championships, Armstrong was the strongest rider in the field but he lost because, in the words of the US team physician, "he wasn't mad at anybody". This is a mistake that he has seldom repeated since. Whether it is doctors saying that he will never fully recover from cancer or journalists decreeing that he is too old to win the Tour at 37, he is fuelled and inspired by the desire to prove people wrong. And that is why, if you were Alberto Contador, Armstrong's main rival in this year's race, and inconveniently his team-mate, you would be very, very scared.